This problem occurs on a John Deere L110 lawn tractor. The engine starts and runs with the throttle in the start position. As soon as the throttle is moved to the 'run' position, the engine stops. If I move the throttle back to the start position before the engine completely stops, the engine recovers and continues to run. I suspect the simple electronics think I am vacating the seat or trying to mow while in reverse. Is there a simple way to test my theory? Thanks!

The start position likely kicks in the choke and the run position is full throttle with no choke. I think you are not getting enough fuel. Drop and clean the bowl and needle valve, drain the fuel and add freshly bought fuel. Tell us how it goes after